Motorsport Plumbing Systems: System Overview
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System Overview
10.57
| 00:00 | Fundamentally the sole purpose of our vehicle's braking system is to slow the car down, and this is achieved by transferring the vehicle's kinetic energy to thermal energy through the use of friction. |
| 00:12 | The source of the friction that makes this energy exchange possible in modern brakes comes from a consumable material being pressed against a solid rotating surface. |
| 00:22 | In all modern braking systems, this will be in the form of brake pads being squeezed against a brake disc. |
| 00:28 | Because this friction force is applied at a distance from the centre of rotation of the brake disc, this leads to a torque that acts to slow down the speed the brake disc is turning at. |
| 00:38 | The brake disc is mechanically connected to the wheel and tyre assembly, therefore they exert a force on the road surface, slowing the car down. |
| 00:47 | Drum brakes, although not common in performance applications, use slightly different arrangement to this but the effect is essentially the same. |
| 00:55 | In either case, the system begins with a brake pedal. |
| 00:59 | The force applied to the brake pedal by the driver is the primary means of controlling the brake force. |
| 01:05 | The brake pedal will have a mechanical linkage that applies force to a hydraulic master cylinder. |
| 01:11 | In road cars there is generally a brake booster device, otherwise known as a brake servo, between the brake pedal and master cylinder. |
| 01:19 | The purpose of the brake booster is to reduce the amount of force required by the driver to actuate the brakes. |
| 01:25 | In motorsport applications we often don't use a brake booster, instead we'll use a dual master cylinder arrangement with a bias bar to allow for brake bias adjustments by the driver. |
| 01:37 | The master cylinder is full of hydraulic fluid. |
| 01:40 | With force applied, hydraulic pressure is built up inside the main chamber. |
| 01:44 | This hydraulic pressure is transferred to the brake callipers via the brake lines which are often made up of both solid and flexible sections. |
| 01:53 | Flexibility is required in some parts as the brake callipers will generally move with the suspension. |
| 01:58 | Pressure sensors are commonly installed at some position on the brake lines and used for various reasons, from something as simple as data logging or potentially as inputs for ABS systems. |
| 02:10 | Proportioning valves and metering valves are also commonly integrated into the factory brake plumbing systems to regulate the pressure to the brake callipers. |
| 02:19 | With the hydraulic pressure now transferred to the brake callipers, the pistons inside the callipers are forced out of the calliper body. |
| 02:26 | These pistons press against the brake pads, one side of which has a sacrificial friction material applied to it. |
| 02:33 | This is the side that's squeezed against the rotating brake disc to provide our brake torque. |
| 02:38 | For our discussions, this plumbing between the master cylinders and the brake callipers is our main focus. |
| 02:44 | It conveys the brake fluid and transfers hydraulic pressure through the system. |
| 02:49 | Nearly all modern vehicles also have ABS or anti lock braking systems from the factory. |
| 02:55 | The main components in an ABS system are the pump, wheel speed sensors, brake pressure sensors, steering angle sensors, G sensors, gyros and the ABS control unit. |
| 03:07 | The ABS pump and sensors are plumbed in line with the main braking system. |
| 03:12 | With the master cylinder outlets being connected to the pump. |
| 03:16 | From here, the pump is responsible for modulating the brake pressure to each brake calliper. |
| 03:22 | So the plumbing doesn't change much from the standard arrangement. |
| 03:25 | But in reality, if you're retaining the factory ABS, it's unlikely you'll be making significant changes to the plumbing anyway. |
| 03:33 | One last thing that's worth mentioning here is the primary routing options for brake lines. |
| 03:39 | In some OE applications, brake lines are routed diagonally. |
| 03:43 | Meaning the front left and rear right are on one circuit and the front right and rear left are on another. |
| 03:49 | This means that if there is a hydraulic leak in one circuit, at least one of the front brakes will be able to provide some stopping force. |
| 03:57 | This is important as the front brakes always provide more total stopping power when compared to the rear. |
| 04:04 | Of course the downside here is that the car will be difficult to control during braking as the brake force is uneven side to side. |
| 04:12 | The conventional way that a motorsport style braking system is laid out is for the front and rear systems to be plumbed separately. |
| 04:20 | As we discussed, this can be used with a dual master cylinder and bias bar pedal box to allow us to modify the front and rear brake bias. |
| 04:29 | What's important to understand is that within each circuit, the pressure is essentially the same regardless of the location, be it in the master cylinder, in the brake line or in the caliper. |
| 04:40 | So, often we'll run one line from the master cylinder towards the axle of the vehicle and then split it to each caliper to avoid extra unnecessary plumbing. |
| 04:50 | Compared to our other plumbing systems, the internal fluid pressure can also be very high, particularly with ABS. |
| 04:58 | In motorsport applications where we generally use much higher pedal effort, it's possible to see more than 2000 psi. |
| 05:06 | As a result, and relevant to the function of the brakes, is something referred to as compliance. |
| 05:12 | To the driver, excessive compliance results in more pedal travel being required to build a given amount of brake pressure. |
| 05:20 | This will often be described as a soft, spongy or long brake pedal. |
| 05:24 | It's not a nice sensation and quickly destroys a driver's confidence in the brakes. |
| 05:29 | In extreme cases, this can result in the pedal reaching its maximum mechanical travel before sufficient brake pressure is reached, with obvious dangerous consequences. |
| 05:41 | Compliance can be caused by a lack of stiffness in components like the pedal box and calipers, but more relevant to our discussions around plumbing, it can also be caused by our line swelling and increasing in volume with pressure. |
| 05:54 | We'll discuss this further in the next module but naturally this is something we want to minimise as much as possible. |
| 06:01 | Related to this and one of the main properties of brake fluid that we care about is its compressibility. |
| 06:07 | That is, we want to minimise any volume change of the internal fluid when pressure is applied. |
| 06:13 | The lower the compressibility of our brake fluid, the less compliance we'll have. |
| 06:18 | Of course, leading to more direct action between the driver's pedal input and the brake caliper force. |
| 06:24 | To some extent, the chemistry of different brake fluids does affect its compressibility. |
| 06:29 | But compressibility becomes the biggest problem when the brake fluid is heated above its boiling point. |
| 06:35 | When this occurs, small air bubbles start to form inside the fluid. |
| 06:39 | Air is much more compressible than brake fluid and therefore results in a lot of compliance. |
| 06:45 | The source of this heat that causes the brake fluid to boil comes from the thermal energy absorbed by the brake calipers during braking events. |
| 06:54 | While the discs may operate at 800 degrees Celsius or more, the brake calipers operate at much lower temperatures. |
| 07:02 | With that said, this still makes controlling caliper temperatures and choosing a suitable brake fluid critical in avoiding boiling situations. |
| 07:11 | Most brake fluids are hydroscopic, meaning they absorb moisture and the more moisture present, the lower the boiling point. |
| 07:18 | So, this is something we want to avoid by ensuring the system remains sealed. |
| 07:23 | Brake fluid is also damaged by excessively high temperatures, causing it to break down which also lowers its boiling point. |
| 07:31 | For these reasons, the brake fluid is a consumable item that needs to be changed periodically so our system needs to allow for this as well as the ability for parts to be changed out if required. |
| 07:42 | The DOT or Department of Transport rating of the fluid has an effect on this and other considerations, but if you want to dive any deeper into this topic, I highly recommend checking out our very thorough motorsport braking systems course. |
| 07:57 | When it comes to bleeding of the brake system, generally the process takes place using components such as the reservoirs and bleed nipples on the calipers rather than the aspects of the plumbing. |
| 08:08 | If you're wondering about the best way to carry this out, don't worry, we'll be covering the bleeding process in a dedicated module later in the practical skills section of this course. |
| 08:18 | Aside from our main braking components, there are some other uses of this form of hydraulic fluid plumbing that function in a very similar way. |
| 08:28 | Hydraulic handbrakes, commonly used to lock the rear wheels of rally, offroad and drift cars use a master cylinder which is acted on by a lever arm. |
| 08:36 | The master cylinder is plumbed to the rear calipers and in some cases this will be connected into the existing rear brake lines for what's referred to as an inline setup. |
| 08:47 | The issue here is when the driver tries to use the handbrake and footbrake at the same time, there will be interference. |
| 08:54 | Alternatively, and with the benefit of separating the main braking system and the handbrake circuit, it's common to use a second caliper on each rear wheel with the handbrake master cylinder plumbed to the rear of the vehicle and then each handbrake caliper, commonly referred to as a dual caliper setup. |
| 09:12 | Less common is a single caliper with separate pressure systems, one dedicated to the main braking system with its own set of pads and another for the handbrake with another set of pads. |
| 09:24 | Naturally these will need separate plumbing circuits but the advantage is the decoupling of the systems with the packaging of a conventional caliper setup. |
| 09:33 | Finally, the clutch in manual transmission vehicles also makes use of a very similar plumbing system and generally the same hydraulic fluid. |
| 09:42 | The clutch pedal will act on its own master cylinder, which will be plumbed to a clutch slave cylinder that could act directly on the clutch or through some other form of mechanical linkage. |
| 09:54 | Regardless, the same concerns around compliance apply. |
| 09:57 | The ideas in the following modules about materials, routing and heat management can also be applied to the clutch plumbing system. |
| 10:06 | And that covers about everything we need to know about our braking system so let's quickly go over the main points from this module. |
| 10:13 | Hydraulic fluid is used to transfer force from the driver input at the pedal to the brake calipers. |
| 10:19 | In motorsport applications, this is generally done using a dual master cylinder arrangement with one circuit for the front brakes and one for the rear. |
| 10:29 | The compressibility of the fluid and resistance to volume change is related to the primary concern of reducing compliance in the system. |
| 10:38 | While the fundamental layout of the system is common amongst many different setups, the integration of ABS and hydraulic handbrakes come with additional considerations. |
| 10:49 | The same plumbing is also appropriate for the use of clutches in manual transmission vehicles. |
